The present invention relates to a powder capable of being used as a thermal energy storage material.
Certain polymeric materials have been examined in the prior art for thermal energy storage for home heating and cooling applications. A candidate material is a lightly cross-linked high density polyethylene in the form of pellets. The crosslinking is necessary to prevent the pellets from sticking together when heated above the melting point.
The following three methods of controlled chemical crosslinking of high density polyethylene have been reported in Salyer, I. O. and Davison, J. E., "Thermal-Energy Storage in Crosslinked Pellets of High-Density Polyethylene for Home Heating and Cooling via Off-Peak Electric Power Utilization", J. Appl. Poly. Sci., 28, 2903, 1983. The first method relates to peroxide-initiated, free radical crosslinking. The second and third methods, respectively, relate to vinyl triethoxy silane grafting crosslinking and electron beam crosslinking. In all of these cases, the crosslinks eliminate the melt flow which is desirable for high-temperature form stability. However, undesirably, these processes decrease crystallinity and heat of fusion which is highly desirable for thermal energy storage. All three methods of crosslinking were reported to result in losses of up to thirty percent of the initial heat of fusion.
Heretofore, crosslinking particles of high density polyethylene has resulted in a considerable loss in the heat of fusion as compared to the uncrosslinked particles. Thus, the thermal efficiency of a thermal energy storage system using such particles is undesirably reduced.